This invention relates to a method and an apparatus for determining a point of regulation for drafting units integrated in a fiber processing machine and is of the type in which the change of a quality-characterizing magnitude of the fiber material (for example, its thickness, mass or the like) is measured. The measurement signals are applied to a control device for varying the draft.
The invention is particularly concerned with an evening of textile slivers in drafting units associated with fiber processing machines. In preparation machines frequently a drafting unit is provided in the feed chutes. Likewise, in carding machines or roller cards regulated drafting units may be disposed in the feed chute or in the inlet zone of the machine. At the input of carding machines or roller card units sensors are provided which detect the thickness of the fiber batt and, as a function of the sensed magnitudes, control the rpm of the feed rolls for evening the fiber batt. At the outlet of the carding machines or roller card units sensors are provided for monitoring the sliver mass. The signals corresponding to the sliver mass fluctuation may be used to regulate the feed roll at the input of the machine or to control a drafting unit at the outlet of the machine.
In the regulated draw frames of spinning systems such as cotton spinning, yarn spinning, half yarn spinning, woolen spinning and bast fiber spinning systems, the slivers are caused to converge and are subsequently drafted. During the drafting in the drafting unit, sliver mass fluctuations are compensated for by regulation. In regulated draw frames as well as in carding machines and roller card units, both the control and the regulating principles find application. According to the control principle the sensor for the sliver mass fluctuations is situated upstream of the drafting unit. In the regulating principle, such sensor is positioned downstream of the drafting unit. In either case the signal representing the sliver mass fluctuation is utilized for changing the draft in the principal drafting field.
The detection of mass fluctuations, particularly thickness fluctuations, is effected as a rule with a mechanical scanning system upstream of the input of the draw unit (drafting unit). The measuring signal is stored and after a predetermined delay which corresponds to a certain displacement of the processed material, the regulation is initiated which compensates for the mass fluctuations. Such a point of initiation in time is the point of regulation. The compensation of the mass fluctuations in the principal drafting field is effected by changing the rpm of the regulating motor while at the same time the rpm of the drive motor for the output rolls of the principal drafting field is maintained constant.
Known methods and devices concern the exact preservation of the point of regulation and its correction, while taking into account internal machine effects and/or environmental effects, as disclosed, for example, in German patent documents 42 15 682 and 43 06 343. Further proposals in the prior art concern the effect of the starting and stopping of the regulated draw frames or the inertia behavior of the scanning members and structural groups for driving the rolls of the draw frame. According to European Published Patent Application 803 596, to which corresponds U.S. Pat. No. 5,771,542, setting values for the point of regulation and/or the amplification are determined. In such a system the point of regulation in a test or setting process prior to operation of a draw frame or a carding machine is determined and maintained during operation. The proposals of the prior art are based substantially on maintaining constant the point of regulation during operation. Changes occur only during the preliminary setting steps performed for the machine.
Melliand Textilberichte (Melliand Textile Bulletins), in Volume 79 (1998), pages 403, 404, describe that the behavior of fiber motion in the drafting fields is substantially dependent from the delivery speed. As a rule, at low speeds a uniform fiber motion occurs. At higher speeds, however, a sudden acceleration is experienced in the middle of the drafting field. It has been observed that the speed conditions of the fiber are less constant as viewed along the width of the material and also as a function of time. In addition, in one part of the fibers, accelerations and decelerations alternate in a more pronounced manner, that is, the fiber acceleration is not continuous. These effects may be traced back to an increase of the alternation of sliding/adhering properties and sliver thickness fluctuations. These fluctuations of the fiber motion render the slivers non-uniform.
It is an object of the invention to provide an improved method and apparatus of the above-outlined type from which the discussed disadvantages are eliminated and which, in particular, provides for a significant improvement in the degree of efficiency of regulation and the uniformity of the drafted sliver and, in particular, the regulating process is additionally optimized.
These objects and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the apparatus for determining a point of regulation in a drafting unit includes a sensor for generating signals as a function of change in a quality-representing magnitude of the fiber material running through the drafting unit; a control device receiving the signals for varying a draft of the fiber material by the drafting unit; and an arrangement for continuously determining, during operation, optimal points of regulation based on the signals.
Thus, according to the invention, the point of regulation is varied during the production process as a function of mass fluctuations to thus significantly improve the efficiency of regulation. According to the invention, first data concerning the mass fluctuation are stored and subsequently, based on the stored values, the optimal points of regulation are determined with the aid of a computing algorithm or by a transfer function. Dependent on the results, to each sliver thickness a point of regulation is assigned. In this manner the point of regulation is variable during operation of the sliver drawing unit.
A microprocessor is expediently used for computing the optimal point of regulation. The detected mass fluctuations which are essential for changing the rpm of the regulating motor and the computed points of regulation associated therewith are stored and are accessed upon reaching the respective point of reaction. The nominal rpm is applied to the regulating motor preferably via a frequency converter. The position of the regulation and thus the extent of displacement from the measuring location associated therewith up to the point of reaction is variable independently from the fiber material.
The particular properties of the fiber materials, for example, the static and dynamic friction behavior as well as type of material may be added into the computing algorithm or the transfer function.
It may be advantageous from the point of view of drafting theory to perform the sliver mass regulation as late as possible in the spinning process. Thus, German patent document 34 25 345 proposes to provide a regulating device in the opening units of open-end spinning machines. Such a solution, however, has not yet been used in the mass producing practice because of cost considerations. The invention may be advantageously utilized in opening units of open-end spinning machines. Here too, first the data on sliver mass fluctuations are stored and subsequently, based on the stored values, the optimal points of regulation are determined with the aid of a computing algorithm or a transfer function so that, according to the results thereof, to each measurement of sliver a point of regulation is assigned. In this manner, the point of regulation is variable during the operation of the regulated draw unit.
The invention, in addition to drafting units of preparation machines, draw frames and open-end spinning machines, may be utilized in draw units of other types of spinning machines, such as flyers, ring spinning or air spinning machines. Such draw units have been heretofore not equipped with regulating devices on a basis of mass manufacture because of cost considerations. From the point of view of drafting technology, the use of a regulating device according to the invention with continuous computation of the point of regulation is a sensible solution.